Without question, the Sony a7S III is a mirrorless camera meant for video. Impressive specs and image quality are wonderful, but it has the same problems for video as every other mirrorless camera: its form factor is better suited to stills. One solution is to get a cage, such as this Master Kit from SmallRig that I was able to take for a spin.
It’s the Small Things
When it comes to relatively simple devices and accessories, it really is the small things that make the biggest difference. For a camera cage, that is the ease of attachment, the placement of particular mounting points, and various other details that make it a true extension of the original device. Most importantly, it shouldn’t get in the way of any controls or ports.